Key changer and tremolo for guitar



April 8, 1969 A. A. KRAFT 3,437,0m

KEY CHANGER AND TREMOLO FOR GUITAR Filed April 19, 1966 Sheet of 3 40 7%GD 44? |i. 1

I NVENTOR 49 7/102 4 /(@4F7 April8, 1 969 A. A. KRAFT 3,437,001 KEYCHANGER AND TREMOLO FOR GUITAR Filed April; 19, 1966 Sheet 3 .013'

April 8, 1969 A, KRAFT 3,437,001

KEY CHANGER AND TREMOLO FOR GUITAR Filed April 19, 1966 Sheet 3 of 5 fZZZ/Z INVENTOR.

427/102 4. KP/IFr United States Patent Oifice 3,437,001 KEY CHANGER ANDTREMOLO FOR GUITAR Arthur A. Kraft, Riverside, Califl, assignor offorty-nine percent to George J. Hefiley, Riverside, Calif. Filed Apr.19, 1966, Ser. No. 543,587 Int. Cl. Gd 3/14 US. Cl. 84-312 10 ClaimsABSTRACT OF THE DISCLOSURE Guitar strings are attached at their bottomends to a rockshaft by adjustable means whereby each string is tangentto a circle concentric with the rockshaft, and the radius of said circlecan be increased or decreased by adjustment so that turning therockshaft causes all strings to maintain correct tonal relationship withone another as their pitch changes. The rockshaft can be oscillated byeither a tremolo arm or a key-change control. A second rockshaft isconnected to the first by springs, which oppose the torsional effect ofstring tension, and is rotated simultaneously with the first in thedirection to increase spring tension when the opposing spring tension isincreased.

The present invention relates to string instruments of the lute class,such as guitors, mandolins, and the like, having a long fretted neck anda plurality of strings that are plucked by the player, while the pitchof the strings is varied by placing the fingertips of one hand atdifferent positions along the neck.

The primary object of the invention is to provide means for raising orlowering the pitch of all strings on an instrument of the classdescribed, while maintaining correct tonal relationships of the stringsrelative to one another. Thus, all of the strings may be raised orlowered in pitch by one or more frets, without any of the stringsgetting out of tune with respect to the others. It is desirable to beable to raise or lower the pitch of the strings in this manner, toenable the player to get his instrument in tune with the rest of anorchestra or with another accompanying instrument, where there may be avery slight discrepancy in tune, without individually adjusting all sixstrings (or whatever number of strings the instrument may have).

It may also be desirable at times to raise or lower the pitch of theinstrument by one or more frets toaccommodate the vocal range of asinger, so as to permit playing a number in a sharped or flatted key,using the standard pitch finger position. This eliminates the necessityof barring all six strings with one finger in order to change key, orusing a clamp bar, known as a capo. Another reason for changing pitch isthat, under certain conditions, an instrument will seem to have bettertone quality when the pitch is lowered a fret or two in cases where theinstrument is being played by itself. This may be due to the fact thatcertain strings on the instrument are too tight for best tone when tunedto standard pitch, and the appropriate change of tension will correctthis condition by softening the strings.

To change the pitch of the strings, without changing length, requires achange in tension. This may be accomplished by attaching the anchoredends of the strings to a rockshaft, which is turned slightly in onedirection or the other, to increase or decrease the tension in all ofthe strings. If all of the strings are stretched (or relaxed), by thesame amount, they will all be raised (or lowered) in pitch, but not bythe same amount for each string. This is because the strings are allunder different amounts of initial tension, and they are of differentdiameters and tempers. Thus, an adjustment of the rockshaft to pro ducea one-fret increase in tone in one string, may pro- Patented Apr. 8,1969 duce a slightly greater or slightly lesser increase in all of theother strings. This slight discrepancy in tone adjustment of the severalstrings is overcome in the present instrument by having the stringstangent to the rockshaft at different radial distances from the centerthereof. Thus, if we assume for the purpose of illustration, that afirst string requires one unit increment of stretch to raise its pitchby one fret, and this first string is tangent to the rockshaft at oneunit distance from the center thereof; then a second string requiringhalf a unit increment of stretch to raise its pitch by one fret would betangent to the rockshaft at half a unit distance from the centerthereof.

The concept of using different diameters on a rockshaft, over which thestrings are passed, is not entirely new. However, it has been found thatstrings vary greatly in physical properties such as gage, temper, andmetallurgical composition, so that in replacing one string with anothersupposedly of the same kind, it will be found that the rockshaftdiameter that was perfect for the discarded string is no longer perfectfor its replacement. As a result, the rockshaft having different fixeddiameters is of limited utility, and will perform satisfactorily onlywhere strings are carefully selected for that purpose. Since it is notalways possible to select strings from a large assortment, thisshortcoming of the rockshaft having different fixed diameters is adistinct handicap.

Another important object of the invention, therefore, is to provide apitch-changing mechanism for a stringed instrument of the classdescribed, having a rockshaft to which the strings are attached, andalso having means for varying the radial distance from the center of therockshaft to its point of tangency with each of the strings. In thisway, the radial distance from the center of the rockshaft to its pointof tangency with any one string can be precisely adjusted to give thatstring the exact amount of stretch required to raise or lower its pitchby one fret when the rockshaft is turned through an angular distance toraise or lower the pitch of the other strings by one fret.

Another object of the invention is to provide a pitchchanging mechanismfor a stringed instrument, as described, wherein the strings are trainedaround and attached to rockshaft, and means are provided forcounterbalancing the torsional effect of the string tension on therockshaft, whereby any pitch adjustment is accomplished without havingto overcome the tension in the strings. An added feature of theinvention is that the counterbalancing torsional means is adjustable, sothat the tension of the springs can be cancelled out to any desireddegree. This is important for the tremolo-producing device, which mustbe relatively effortless to operate.

A further object of the invention is to provide a stringed instrument ofthe class described, wherein the pitch of the strings can be changedquickly and easily by a simple adjustment of a pitch control member,such as a knob or wheel on the instrument body, without af fecting theadjustment of the tuning pegs of the individual strings.

Another object of the invention is to provide a stringed instrument ofthe class described, having manually operable means for rapidly andcontrollably increasing or decreasing the tension of the strings whilethe instrument is being played, for the purpose of slurring notes orchords up or down from standard pitch, or to produce a tremolo effect.More specifically, it is an object of the invention to provide such ameans for varying the tension in the strings while preserving thecorrect tonal relationship between the several strings, so that if achord has been struck, it will retain its harmonious quality and willnot become discordant during the pitch change.

A further object of the invention is to provide a tremolo-producingdevice which can be operated selectively to oscillate the pitch of thestrings either upwardly from standard pitch, or downwardly therefrom.

Another object of the invention is to provide a stringed instrument ofthe class described which can be manufactured and sold with thepitch-changing feature but without the tremolo-producing feature, orwith the tremolo-producing feature but without the pitch-changingfeature, and to which the other feature can be added at a later datewith only a relatively minor bit of structural change in the instrument.

FIGURE 1 is a top plan view of a guitar constructed in accordance withmy invention;

FIGURE 2 is an enlarged, fragmentary elevational view of the pitchchanging mechanism of the present invention, which is partially cut awayto reveal some of the underlying structure;

FIGURE 3 is a sectional view of the same, taken at 3-3 in FIGURE 2;

FIGURE 4 is another sectional view, taken at 44 in FIGURE 2;

FIGURE 5 is a sectional view of a detail, taken at 5-5 in FIGURE 2;

FIGURE 6 is a sectional view of another detail, taken at 6-6- in FIGURE2;

FIGURE 7 is a side elevational view of the pitch changing mechanism, asseen from 77 in FIGURE 2;

FIGURE 8 is an enlarged fragmentary sectional view, taken at 88 inFIGURE 7;

FIGURE 9 is an enlarged, partially cut-away elevational view of thecontrol device for raising or lowering the pitch of the strings;

FIGURE 10 is a sectional view through the same, taken at 10-10 in FIGURE9;

FIGURE 11 is a perspective view of one of the anchor devices used toconnect each of the strings to the rocker bar; and

FIGURE 12 is an enlarged sectional view through the rocker bar ofanother embodiment of the invention, similar to FIGURE 4, showinganother means for attaching the strings to the rocker bar, with meansfor adjusting the radial distance from the center of the shaft to thepoint of tangency of the string.

In the drawings, FIGURE 1 shows a typical electric guitar having a body20, and an elongated neck 22 extending from the upper end thereof. Theneck 22 has a plurality of longitudinally spaced, transversely extendingfrets 23 provided in its top surface, and at the outer end of the neckis a head 24 with tuning pegs 25, to which the customary six strings 26are attached. The strings 26 extend lengthwise down over the neck 22 inlaterally spaced, generally parallel relationship, and pass over anelectromagnetic pickup unit 28.

Near the lower end of the guitar, strings 26 are trained over groovedrollers 30 of a roller bridge 31. The rollers 30 are spaced apartlaterally and are screw-threaded onto a cross shaft 32, which issupported betwen the upturned ends 34 of a bracket 36 that is attachedto the body 20. The rollers 30 are rotatable on the shaft 32 so as toroll freely with the strings as the latter are caused to move lengthwisewhile being tightened or sla-ckened, as will be described later. Inpassing over the rollers 30, the strings 26 are bent downwardly at aslight angle, and each string is connected by a link 38 to a rockshaft40 in a manner whereby the said string is tangent to a circle having itscenter at the axis of the rockshaft, as best shown in FIGURE 4. Thecircle referred to is shown in phantom line and is designated by theletter C.

The rockshaft 40 is rotatably supported at its ends in two upstandingsupport plates 42, which are attached to opposite sides of a bracket 44that is mounted on the body 20. Extending diametrically through therockshaft 40 at longitudinally spaced points thereon are six tappedholes 46, and screwed into these holes are adjusting screws 48.

The screws 48 are parallel to one another, and lie in a common planethat is generally perpendicular to the strings 26 for that portion oftheir length below the roller bridge 31. Each of the screws 48 projectsbelow the bottom surface of the rockshaft 40, and formed in theprojecting ends of the screws near their bottom ends are V-shaped,circumferential grooves 50.

Each of the links 38 is preferably stamped out of sheet metal, and isbent to the configuration shown in FIGURE 11. At one end of the link 38is a hole 52 having a knife edge that seats in the bottom of the groove50 in the corresponding screw 48. The diameter of hole 52 issufficiently large to pass the end of the screw 48, and the point ofcontact where the knife edge of hole 52 touches the bottom of theV-groove 50 constitutes the point of attachment of the string 26 to therockshaft. At the other end of the link 38 is a second hole 54 ofsmaller diameter, through which the string 26 passes. The string iswrapped around and attached to a small brass ferrule 56, which preventsthe string from being pulled back through the hole 54. The rockshaft 40is milled ilat at 58 on its underside, to permit the screws 48 to bebacked out so as to adjust the links 38 closer to the axis of therockshaft, than would otherwise be possible if the rockshaft were leftround. Each of the screws 48 has a hexagonal socket in its top end toreceive an Allen wrench for adjustment purposes.

As mentioned earlier, the strings 26 are attached to the rockshaft 40*by links 38 in such a manner that they are, in effect tangent to acircle having its center at the axis of the rockshaft. The diameter ofthe circle depends upon the distance of the V-shaped groove 50 from thecenter of the rockshaft, and this is adjustable over a relatively widerange by advancing or backing out the adjustment screws 48 with respectto the rockshaft. The tension of the strings 26 acting on theirrespective moment arms exerts a powerful torque on the rockshaft,tending to turn the latter in the counterclockwise direction, as viewedin FIGURE 4. To counteract this torque due to string tension, 1 haveprovided a counter-balancing arrangement in the form of a plurality ofcoil springs 62, each of which is connected at one end to the head of ascrew 64 that is threaded down into the rockshaft 40 on the top sidethereof between the screws 48.

The other ends of the springs 62 are connected to the heads of screws66, which are threaded into a second rockshaft 68 located aboverockshaft 40 and parallel thereto. This second rockshaft 68 is supportedat its ends in upturned ears 70 at opposite sides of the bracket 44.Rockshaft 68 lies below the strings 26, and has a plurality oflongitudinally spaced grooves, or channels 72, cut into its top sidebelow each string to provide clearance therefor. Screws 64 and 66 havehexagonal sockets 74 formed in their heads, to receive an Allen wrenchfor adjustment purposes.

Rockshaft 40 projects beyond the right-hand support plate 42 (as viewedin FIGURES 2 and 3), and swingably mounted on the projecting end is adownwardly extending lever arm 76. The lever arm 76 lies flat againstthe outside surface of the right-hand plate 42 and is constrained tooscillate through a limited angular distance by means of two screws 78,which extend through arcuate slots 80 in the lever arm on opposite sidesof the center line thereof. The slots 80 are concentric with the axis ofthe rockshaft 40, and the heads of the screws 78 overlie the outersurface of the lever arm 76 to hold the latter flat against the supportplate 42, while allowing oscillatory movement within the range of theslots.

Laterally outward of the lever arm 76 is a lever arm 82 having a hub 84which is fixedly mounted on the rock shaft 40. A post 86 is screwed intoa tapped hole in the lower end of the lever arm 76, and projectslaterall outwardly therefrom, through the horizontal portion 88 of aninverted, L-shaped slot 90 formed in the lower portion of lever arm 82.Post 86 projects beyond the lever arm 82, and swingably mounted on theprojecting outer end thereof is a bell crank 92, which is best shown inFIG- URE 7.

One arm 94 of bell crank 92 extends upwardly from post 86, and at itsupper end is a pivot screw 96, which is substantially coaxial withrockshaft 40. The pivot screw 96 connects bell crank arm 94 to one endof a link 98, which extends horizontally to the left, as viewed in FIG-URE 7. The other end of link 98 is connected by a pivot screw 100 to theupwardly projecting arm 102, of a bell crank 104 forming the hub portionof the tremolo arm 106.

Tremolo arm 106 is conveniently made of round rod, one end of which isreceived within a bore in the top end of the vertical bell crank arm102, and is free to turn therein. The rod forming the tremolo arm 106extends upwardly, and is bent to extend generally parallel to the topsurface of the guitar body 20. Inserted over the outer end of thetremolo arm 106 is a sleeve 108 of soft rubber or the like, which servesas a handle.

Being free to turn within its bore in the vertical bellcrank arm 102,tremolo arm 106 can be swung over to one side and out of the way, whennot in use. Then, when the player wishes to use the tremolo, he merelyswings the arm 106 inwardly, so that the handle 108 is located at themost comfortable position for vertically oscillating the arm 106 whileplucking the strings 26. The tremolo arm is oscillated in the verticalplane by pressing handle 108 downwardly from a normally centeredposition to raise the pitch of the strings slightly above standardpitch, or by raising the handel 108 to lower the pitch. The means bywhich this is accomplished will now be described.

Bell crank 92 has a second arm 110 extending downwardly and to the rightfrom post 86, as viewed in FIG- URE 7, and mounted on its outer end is ashort, laterally inwardly projecting pivot shaft 112 having a roller 114journaled thereon. The roller 114 is disposed within the verticalportion of the inverted, L-shaped slot 90, and bears against theleft-hand edge 116 thereof (see FIG- URE 6), which lies on a radiusextending through the axis of rockshaft 40. The diameter of the roller114 is a few thousandths of an inch smaller than the width of thevertical portion of slot 90, and therefore the righthand side of theroller clears the right-hand edge of the slot. Thus, the only contact ofthe roller 114 with lever arm 82 is along edge 116.

The slight counterclockwise torque exerted On rockshaft 40 by the excessof tension in string 26 over the tension of springs 62, causes the leverarm 82 to bear against the roller 114, holding slot side 116 against theoutside of the roller. When the bell crank 94 is rocked in the clockwisedirection about post 86, roller 114 travels downwardly and to the left(FIGURES 6 and 7) in an arcuate path, pushing the lower end of lever arm82 to the left. This causes lever arm 82 to rock the rockshaft 40 in theclockwise direction. Clockwise turning of rockshaft 40 causes thestrings 26 to be pulled tighter, and this raises the pitch of thestrings. Since the bell crank 94 is rocked in the clockwise direction bypressing the tremolo arm 106 downwardly from its normal, springcenteredposition, it follows that pressing downwardly on the tremolo arm causesthe pitch of the strings to be raised.

In the same manner, raising the tremolo arm 106 from its normal,spring-centered position, rocks the bell crank 104 in thecounterclockwise direction, pulling link 98 to the left, as viewed inFIGURE 7. This causes the bell crank 94 to be ro-cked in thecounterclockwise direction about the post 86, and swings the roller 114upwardly and to the right, in an arcuate path. Since the lever arm 82 isheld against the roller 114 by the spring torque on rock shaft 40, itfollows that the rockshaft is rotated in the counterclockwise direction,which has the effect of lowering the pitch of the strings from standardpitch.

The tremolo arm 106 is spring-centered in its normal position of rest bytwo centering springs 118, and by a rubber mounting 120 for bell crank104; the latter being shown in cross-section in FIGURE 8. The rubbermounting 120 comprises a sleeve 122 of vulcanized rubber, which isinserted tightly into a bore 124 in the bell crank 104, and insertedtightly into the sleeve 122 is a brass tube 126. Passing through thetube 126 is a screw 128, the inner end of which is threaded into atapped hole 129 in bracket 44 and is locked against turning by a locknut130.

The ends of tube 126 project slightly beyond the opposite side faces ofhell crank 104, and one of said ends abuts against the outer face ofbracket 44, while the other end abuts against the inside surface of aflange 132 on bracket 44. Flange 132 extends parallel to the outer faceof bell crank 104, and is the forwardly bent extremity of a flange 134,which projects laterally from the main body of bracket 44, behind thebell crank 104, as best shown in FIGURE 2.

The head of screw 128 is drawn up tightly against the outside of flange132, thereby clamping the latter tightly against the outer end of tube126. Tube 126 is thus clamped tightly between the outer face of bracket44 and flange 132, and is held against turning. When bell crank 104 isrocked in either direction by the tremolo arm 106, the rubber sleeve 122is stressed in shear, since the outer surface of the sleeve is firmlyadhered to the surface of the bore 124 in the oscillatable bell crank,while the inner surface of the sleeve is firmly adhered to thestationary tube 126. Being thus stressed in shear, the rubber sleeve 122exerts a resilient torsional force on the bell crank tending to returnthe latter to its initial position. There is no sliding fraction betweenthe bell crank 104 and the stationary tube 126 as a result of theirrelative rotational movement, and therefore the bell crank is returnedall of the way back to its original position by the rubber sleeve whenthe tremolo arm is released, with no hysteresis lag.

As best shown in FIGURE 7, the two centering springs 118 are connectedat one end to a second arm 136 on the bell crank 104, and at the otherend to a bracket 138. Bracket 138 has a link 140 connected thereto forvertical swinging movement about a pivot screw 142. Projecting from thetop and bottom sides of the link 140 are two screw heads 144, to whichthe springs 118 attach at one end. The other ends of the springs areattached to screw heads 146, which project from the top and bottom sidesof a second link 148 that is connected by a pivot screw 150 to thebifurcated outer end of hell crank arm 136. Link 148 is also swingablevertically in the same plane as link 140, and the two links tend toalign themselves parallel to a line connecting the centers of pivotscrews 142 and 150.

The pull of springs 118 exerts a yielding spring force on arm 136,tending to pull pivot screw 150 to a position in line with the centersof screws 128 and 142. This is the normal, spring-centered position ofthe bell crank 104, and any time that the bell crank is deflected fromthis position, the springs 118 exert a force tending to restore the bellcrank to its initial position, aided by the action of the rubbermounting 120.

Means is provided for changing the pitch of the strings 26, so as toraise or lower the pitch of all six strings by one or two frets, asdesired. Such pitch-changing means is designated in its entirety by thereference numeral 152, and includes an adjustment lever 154 on the topsurface of the body 20 at the upper right-hand corner thereof.Adjustment lever 154 is fixed to the top end of a short shaft 156, whichis journaled in aligned bushings 158 and 160, that are pressed intoupper and lower plates 162 and 164, respectively. Upper plate 162 isgenerally rectangular in configuration and is secured to the guitar body20 by screws 166. Lower plate 164 is considerably smaller than plate 162and is generally triangular in shape.

7 Plate 164 is connected to plate 162 by three posts 168.

Shaft 156 has an eccentric disk 170 formed thereon at its midpoint, thetop side of which lies flat against the underside of a connecting link172 at one end thereof. The top end of shaft 156 passes through a holein link 172 and through the upper bushing 158, while the bottom end isreceived within the lower bushing 160. A ring 174 is secured by screwsto the underside of link 172, and this ring encircles the eccentric disk170 and has an inwardly projecting radial flange that overlies themarginal edge of the disk, whereby the eccentric disk is free to turnwithin the space defined between the link 172 and ring 174, while thering follows the orbit of the eccentric disk.

The other end of link 172 is connected by a pivot bolt 176 to a sector178. Sector 178 is pivotally connected to the top plate 162 by a pivotbolt 180, and is swingable in a plane parallel to plate 162. Sector 178has two arcuate slots 182 formed therein, which have their centers atthe center of pivot bolt 180, and passing through these slots are screws184, having heads which overlie the bottom surface of the sector alongthe marginal edges of the slots. Screws 184 hold the sector flat againstthe underside of plate 162, while permitting the sector to oscillatewithin the range of the slots 182.

Fixed to the underside of the sector 178 is a radially extending bar185, the outer end of which projects beyond the arcuate edge of thesector. A screw 186 is screwed into the outer end of the bar 185 on thebottom side thereof, with its head passing downwardly from the undersideof the bar. The screw 186 is adapted to be received within a keyholeslot 188 on one end of a push rod 190.

The other end of push rod 190 has another key hole slot 192 formedtherein, which receives a screw 194 that is screwed into the lower endof a lever arm 196. Lever arm 196 is fixed to the right-hand end ofshaft 68 (as viewed in FIGURE 2), and extends downwardly therefrom.About midway between its ends, the lever arm 196 is connected by a pivotscrew 198 to one end of a link 200. The other end of link 200 isconnected by post 86 to the lower end of lever arm 76, and controls theswinging movement of the latter. Thus, when push rod 190 is moved to theleft (FIGURE 5), lever arm 196 and shaft 68 are rocked in the clockwisedirection through a certain angular distance, while lever arm 76 is alsorocked in the clockwise direction through an angular distance about halfthat of lever arm 196. Lever arm 76 is connected to rockshaft 40 in amanner to be described presently, whereby the rockshaft is caused toturn with the lever arm 76 when the latter is swung by link 200, yet therockshaft is free to turn with respect to the lever arm 76 while thelatter is held stationary by link 200.

The differential in angular distance traveled by shaft 68 over thattraveled by rockshaft 40, is the result of the connecting linkage thatjoins them together. The moment arm from the center of shaft 68 to screw198 is only about half the moment arm to screw 194, whereas the momentarm from the center of rockshaft 40* to post 86 is slightly greater thanthe moment arm from the center of shaft 68 to screw 194. The result isthat when shaft 68 is turned by push rod 190, rockshaft 40 is caused toturn in the same direction but through a smaller angular distance thanshaft 68. Thus, when the strings 26 are tightened by turning therockshaft 40 in the clockwise direction, the springs 62 arecorrespondingly stretched to increase their tension, due to the greaterclockwise rotation of shaft 68, which causes screw heads 66 to move awayfrom screw heads 64. In like manner, when the strings 26 are loosened byturning the rockshaft 40 in the counterclockwise direction, the springs62 are correspondingly slackened to decrease their tension, due to thegreater counterclockwise rotation of shaft 68, which causes screw heads66 to move toward screw heads 64.

The driving connection between lever arm 76 and rockshaft 40 is asfollows: Post 86 is mounted on the lower end of lever arm 76 and moveswith the latter in an arouate path, the center of which is located onthe axis of rockshaft 40. Bell crank 94 is pivotally mounted on post 86,and therefore swings with the latter in an arcuate path about pivotscrew 96, which is coaxial with rockshaft 48, and which is heldstationary by link 98. Roller 114 is mounted on bell 94 and movestherewith in an arcuate path having its center at the axis of pivotscrew 96. Since roller 114 is confined within the vertical portion of L-shaped slot 90, it follows that lever arm 82 and rockshaft 40, to whichit is fixedly attached, are caused to rock through the same angulardistance and in the same direction as lever arm 76.

It will be noted in FIGURES 5 and 9 that the large ends of the keyholeslots 188 and 192 are at the outer ends of the push rod 190, and thatthe smaller ends of the slots extend inwardly toward one another. Thisis because the push rod is maintained under compression at all times bythe torque on shaft 68 caused by the tension of springs 62. As describedearlier, the counterclockwise torque on rockshaft 40 caused by thetension of strings 26 is opposed and substantially cancelled out by theclockwise torque of springs 62. Thus, lever arm 76 has only aninsignificant amount of torque exerted on it by post 86. However, leverarm 76 is connected by link 200 to lever arm 196, and the latter isfixedly mounted on shaft 68, which has a considerable counterclockwisetorque exerted on it by springs 62. As a consequence, lever arm 196exerts a force on push rod 190, tending to push the latter to the right,as viewed in FIGURE 5.

The thrust force on push rod 190 toward the right (FIGURE 5) due to thecounterclockwise torque of shaft 68 is opposed by a substantially equaland opposite force exerted on section 178 by two springs 202 and 204.Springs 202 and 204 are attached at one end to pins 206 fixed to theunderside of plate 162, and at the other end to pins 208 fixed to thebar 185. These springs exert a counterclockwise torque on sector 178,which is applied to the right-hand end of push rod 190 as a thrust forcedirected to the left.

The operation of the invention is as follows: The strings 26 of theguitar are first tuned to standard pitch, using the tuning pegs 25. Atthis time, the pitch-changing lever 154 is turned to an intermediate,standard pitch position. When the strings are tuned to standard pitch,they produce the following tones, reading from left to right in FIGURE1: E, A, D, G, B, and E. To lower the pitch by one fret (i.e., onehalf-note), the pitch-changing lever 154 is turned counterclockwise toan appropriate index mark on plate 162, as illustrated in FIGURE 1. Thiscounterclockwise turning of lever 154 causes the push rod 190 to bemoved to the right (FIGURE 9) which turns the rockshaft 40 in thecounterclockwise direction (FIG- URE 5), thereby slackening the strings.The strings should now produce the following tones: E-fiat, A-flat,D-flat, G-flat, B-flat and E-flat. If they do not, the adjustment screws48 are turned in the appropriate direction to bring the strings intotune. For example, if one of the strings is slightly higher in pitchthan it should be, after turning lever 154, the corresponding screw 48would be turned in the direction to increase the distance from thecenter of the rockshaft 40 to the point of contact of link 38 with thebottom of groove 50. In like manner, if another of the strings isslightly lower in pitch than it should be, the corresponding screw 48would be turned in the direction to decrease the distance from thecenter of the rockshaft to the point of contact of link 38 with thebottom of the groove 50.

When all of the strings have been re-tuned with the adjustment screws48, the lever arm 154 is turned to the next index mark in thecounterclockwise direction, which drops the pitch of the strings by twofrets (i.e., one full note). The strings should now produce thefollowing tones: D, G, C, F, A, and D. If any of the strings are out oftune at this second position of lever arm 154, they 9 are again adjustedby turning the appropriate adjustment screws 48.

The lever arm 154 is then returned to its standard pitch position, andthe strings are again tuned by using the tuning pegs 25. Usually, thiswill sufiice for tuning and adjusting the guitar, although it may benecessary to repeat the process while turning the lever arm 154 first tothe one-fret-above-standard-pitch position, in which the strings willsound: F, A-sharp, D-sharp, G-sharp, C and F, and then to thetwo-frets-above-standard-pitch position, in which the strings willsound: F-sharp, B, E, A, C-sharp and F-sharp.

When the guitar has been finally tuned and adjusted properly, the pointsof contact of links 38 with the bottoms of grooves 50 will be at variousdistances from the center of the rockshaft 40. As a result, when therockshaft is turned through a given angular distance, each of thestrings is tightened or slackened by an amount directly proportional tothe distance from the axis of rockshaft 40 to the point of contact ofthe link 38 with the bottom of groove 50 in the adjusting screw 48. Thisamount can be adjusted so that for a given angular increment ofrockshaft 40, each of the strings 26 will be raised or lowered in pitchby exactly a half-note or whole-note, depending upon whether theadjustment lever has been turned to one index mark or the other. Theamount of stretch required to change the pitch of a string by ahalf-note or wholenote varies with the diameter of the string, itstemper, and the tension of the string when tuned to standard pitch. Eventwo strings that are nominally the same pitch and supposedly identical,will require different amounts of stretch to increase the pitch by ahalf-note or whole note, and these varying requirements are met by theadjustment screws 48, which enable the stretch to be matched to thestring.

When the tremolo arm 106 is oscillated in the vertical plane by theplayer, bell crank 92 is oscillated about post 86 by link 98, and thiscauses roller 114 to oscillate in an arcuate path. Lever arm 82 followsroller 114 and is oscillated thereby, causing rockshaft 40 to oscillaterapidly, which produces the rapid raising and lowering of pitch of thestrings 26, which is characteristic of the tremolo effect. The tremoloeffect can be obtained by raising the pitch of the strings slightly fromthe playing key, which is done by pressing the tremolo arm downwardlyfrom its spring-centered position, or by lowering the pitch from theplaying key, which is done by raising the tremolo arm away from theguitar body 20.

One feature of the invention is that the guitar can be sold with thetremolo feature but without the pitch-changing feature, or vice versa,and the missing feature can be added at a later date. For example, thepitch-changing device 152 could be omitted, and the lever arm 196 lockedin a fixed position. In this case, the lever arm 76 would be immobilizedby the fixed lever arm 196, and the rockshaft 40 would be oscillatedonly by the tremolo arm 106, acting through link 98, bell crank 94,roller 114 and lever arm 82. At any later date, the owner of the guitarcould add the unit 152, at which time lever arm 196 would be releasedand push rod 190 connected thereto.

On the other hand, if the purchaser wished to buy the guitar with thepitch-changing unit 152 but without the tremolo arm 106, the arm 106,bell crank 104, and centering springs 118 could be omitted from theguitar, and lever arm 82 connected directly to post 86, using a fillerblock to fill the L-shaped slot 90. As thus constructed, the lever arm76 would act on lever arm 82 through post 86, causing the two lever armsto move as one. Then, at any later date, the owner could add thetremolo-producing unit.

Another embodiment of the invention is shown in FIGURE 12, to whichattention is now directed. In this embodiment, parts which are identicalin function to those previously described are given the same referencenumerals with the prime sufiix.

The chief difference between this embodiment and the one described aboveis in the means for connecting each of the strings 26 to the rockshaft40', whereby the distance from the center of the rockshaft to the pointof tangency of the string may be adjusted to obtain the exact amount oftightening or slackening required to raise or lower the pitch of thestring by the desired amount.

In this case, the rockshaft 40' is provided with sloping, upwardlyconverging sides 210, and slidably engaging these sloping sides are theinwardly turned ends 212 of six generally circular collars 214. Each ofthe collars 214 is mounted on the underside of the rockshaft 40' in linewith its respective string 26', and the latter is trained around thebottom side of the collar and then up to an attachment plate 216.Attachment plate 216 is an elongated plate which is secured by screws218 to the top side of the rockshaft. The plate 216 is preferably seatedon top of washers 220, and the latter bear on a flat surface 222 milledinto the top of the rockshaft. The rear edge of the plate 216 has slots224 formed therein, through which the wires 26 are led. The ferrules 56seat on the top side of the plate 216, at the junction of the main bodyof the plate with an upwardly turned edge portion. The forward edge ofthe plate 216 is bent upwardly to form a flange 226, having holes formedtherein, into which the ends of springs 62 are hooked.

The adjustment screw for each of the collars 214 is designated by thereference numeral 230, and extends diametrically through rockshaft 40.The lower end of screw 230 projects beyond a flat surface 232 milledinto the bottom side of the rockshaft, and its extremity is providedwith a shoulder flange 234 and reduced-diameter tip end portion 236.Flange 234 bears downwardly against the top side of an inverted U-shapedclip 238, while tip end portion 236 is seated in a hole 240 in the clip.The sides of the clip 238 extend downwardly on opposite sides of thecollar 214, and provide side flanges which keep the string 26' fromrunning off the collar 214 on either side thereof.

The upper end of the adjusting screw 230 has a hexagonal socket 242provided therein, into which an Allen wrench may be inserted. Plate 216also has holes 244 provided therein directly over each of the adjustingscrews 230, so that the screws are accessible for adjustment purposeswithout removing the plate.

To increase the radial distance from the center of the rockshaft 40' tothe point where string 26 is tangent to collar 214, the screw 230 isturned with a wrench to advance it downwardly into the rockshaft. Thebottom end of the screw 230 pushes the collar 214 ahead of it, and asthe collar moves downwardly, the ends 212 are spread apart by thediverging side walls 210. Spreading the ends 212 apart has the effect ofincreasing the diameter of the collar 214 to match its distance from theaxis of the rockshaft. The adjustment and manner of using thisembodiment of the invention are substantially the same as in thepreceding embodiment.

I claim:

1. A key changing device for a musical instrument of the lute classhaving a body, a fretted neck extending from one end of said body, and aplurality of strings connected to tuning pegs at the outer end portionof said neck, said strings extending longitudinally above said neck andover said body, said device comprising:

a rockshaft mounted on said body near the lower end thereof, saidrockshaft being disposed transverse to said strings;

means for attaching the other end of each of said strings to saidrockshaft in a manner whereby the said string is tangent to a circlehaving its center at the center of said rockshaft;

means for adjustably varying the distance from the center of saidrockshaft to the point of tangency of each of said strings; and

means for turning said rockshaft so as to tighten or slacken all of saidstrings simultaneously and thereby increase or decrease the pitch ofsaid strings;

the adjusted distance from the center of said rockshaft to the point oftangency of each of said strings being such that for any given incrementof angular distance through which said rockshaft is turned, each stringis tightened or slackened by the exact amount required to keep saidstring in tune with the other strings as their pitch is changed.

2. A key changing device for a stringed instrument as set forth in claim1, wherein said means for adjustably varying the distance from thecenter of said rockshaft to the point of tangency of each of saidstrings comprises a plurality of adjusting screws extendingdiametrically through said rockshaft in threaded engagement therewith,each of said screws having means at one end to receive an adjustingtool, and the other end of said screw projecting beyond said rockshaft,each of said means for attaching one of said strings to said rockshaftbeing cooperatively associated with said other end of its associatedadjusting screw.

3. A key changing device for a stringed instrument as set forth in claim1, wherein spring means is connected to said rockshaft to exert atorsional force thereon substantially equal and opposite in direction tothe torsional force exerted on the rockshaft by said strings, and meansfor varying the tension in said spring means in substantially directproportion to the change in tension of said strings as the latter aretightened or slackened by rotating said rockshaft.

4. A key changing device for a stringed instrument as set forth in claim3, wherein said means for varying the tension in said spring meanscomprises a second rockshaft disposed parallel to said first-namedrockshaft, said spring means comprising at least one coil springattached at one end to said first-named rockshaft and at the other endto said second rockshaft, each of said points of attachment being spacedradially from the center of its respective rockshaft in the directiongenerally perpendicular to the line of pull of said coil spring, wherebytension of said coil spring exerts a torsional force on each of saidrockshafts, said means for varying the tension in said spring meanscomprising a driving connection between said first-named rockshaft andsaid second rockshaft whereby said second rockshaft is rotated in adirection and through an angular distance to cause said coil spring tobe stretched when said first-named rockshaft is rotated in the directionto tighten said strings, and to cause said coil spring to be slackenedwhen said first-named rockshaft is rotated in the direction to slackensaid strings.

5. A key changing device for a stringed instrument as set forth in claim1, wherein said rockshaft has a plurality of adjusting screws extendingdiametrically through it in threaded engagement therewith, there beingone screw for each string and said screws being generally perpendicularto said strings and projecting at one end beyond said rockshaft, andlink means connecting each of said strings to said projecting one end ofits associated adjusting screw, the radial distance between the centerof said rockshaft and the point of contact of said link means with saidscrew being adjustable by turning said screw within said rockshaft.

6. A key changing device for a stringed instrument as set forth in claim1, wherein said means for turning said rockshaft comprises a lever fixedto said rockshaft at one end thereof, a manually adjustable pitchcontrol member on said body movable between a standard pitch positionand at least one other position to change the pitch of the instrument toanother key above or below said standard pitch, and force-transmittingmeans connecting said pitch control member to said lever arm whereby 12moving said pitch control member from one of said positions to the othercauses said rockshaft to be rotated, thereby tightening or slackeningsaid strings to raise or lower their pitch. I

7. A key changing device for a stringed instrument as set forth in claim6, including a tremolo arm supported for oscillatory movement, linkagemeans connecting said tremolo arm to said lever arm whereby saidrockshaft may be oscillated by the tremolo arm independently of saidpitch control means, and spring means connected to said tremolo arm andexerting a force thereon tending to return the same to its initialposition when said tremolo arm has been deflected therefrom.

8. A key changing device for a stringed instrument as set forth in claim6, including a tremolo arm supported for oscillatory movement, a secondlever arm swingably supported on said rockshaft closely adjacent saidfirstnamed lever arm, a link connecting said second lever arm to saidpitch control member, a bell crank pivotally supported on said secondlever arm at a point spaced radially from the axis of said rockshaft,means connecting one leg of said bell crank to said first-named leverarm whereby angular movement of said bell crank about its pivot axiscauses said first-named lever arm to swing through an angular distance,thereby rocking said rockshaft, the other leg of said bell crankextending toward the axis of said rockshaft, and a second linkconnecting said tremolo arm to said other leg of said bell cranksubstantially on the axis of said rockshaft, said connection betweensaid second link and said other leg of said bell crank constituting asecond pivot axis for said bell crank coaxial with said rockshaft,whereby swinging movement of said second lever arm responsive tomovement of said manually operable pitch control member causes said bellcrank to swing with said second lever arm about said second pivot axis,thereby swinging said first-named lever arm with it to rock saidrockshaft.

9. A key changing device for a stringed instrument as set forth in claim1, wherein said rockshaft has a plurality of generally circular collarsmounted thereon in line with said strings, each of said strings beingtrained over its respective collar and attached to said rockshaft, andmeans for adjusting the distance from the axis of said rockshaft to eachof said collars at the point where the string is tangent to the collar.

10. A key changing device for a stringed instrument as set forth inclaim 9, wherein each of said collars is split, said rockshaft havingangularly related flat sides provided thereon which diverge in thedirection toward said collar, the ends of said collar bearing on saiddiverging sides, and adjustment screws extending diametrically throughsaid rockshaft in threaded engagement therewith, each of said screwsprojecting beyond said rockshaft and bearing against the inner surfaceof said collar approximately midway between the ends thereof, saiddiverging sides causing the ends of said split collar to spread apart assaid collar is moved away from the axis of said rockshaft, therebyincreasing the radius of curvature of said collar to approximate thecurvature of a circle concentric with said rockshaft and tangent to saidstring.

References Cited UNITED STATES PATENTS 10/1953 Barr 84--312 3/1966Moseley 843l3 US. or. X.R. 84--313

